An Annual Zonally Averaged Hemispherical Climatic Model with Diffuse Cloudiness Feedback

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  • 1 Department of Biophysical Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14226
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Abstract

An annual, zonally averaged, steady-state hemispherical climatic model is developed which incorporates the diffuse thin cloud tropospheric structure of Weare and Snell as a cloudiness feedback mechanism. The zones are 15° wide and the meridional energy transport is parameterized as that carried by the ocean and by tropospheric eddies, each using a single coefficient, and that carried by the mean annual circulation embodying four coefficients. The radiative transfer calculations through the atmosphere employ the Eddington approximation for the visible spectrum, using the appropriate annual averaged solar zenith angles and the Rodgers emissivity technique for the infrared. Ozone, above the troposphere, is assumed to act only as an absorber in the visible. In the infrared it is assumed to have a constant-hemispherical emissivity at the “tropopause” temperature (212 K). Surface reflectivities in terms of land and ocean are zonally set and land snow and ocean ice lines are calculated to occur at 273 and 263 K at sea level, respectively.

The response of the model to variations in various climatic determinants is studied, including hemispherical variations in carbon dioxide, aerosol and solar constant, and also including certain zonal variations in man-made thermal energy and aerosol. The model characteristically exhibits a poleward amplification of changes in sea level temperature. Polar zone sea level temperature changes are 2–4 times the hemispherical mean. The sensitivity of the model in terms of the hemispherical mean sea level temperature is about twice that of the globally averaged model of Weare and Snell. It is still more stable than models not incorporating cloudiness as a feedback mechanism. The model exhibits three steady-state solutions when the solar constant is in the range 0.805–0.790 times present day. In this range the solutions with the intermediate sea level temperature for a given value of the solar constant are unstable. All other solutions appear stable.

Abstract

An annual, zonally averaged, steady-state hemispherical climatic model is developed which incorporates the diffuse thin cloud tropospheric structure of Weare and Snell as a cloudiness feedback mechanism. The zones are 15° wide and the meridional energy transport is parameterized as that carried by the ocean and by tropospheric eddies, each using a single coefficient, and that carried by the mean annual circulation embodying four coefficients. The radiative transfer calculations through the atmosphere employ the Eddington approximation for the visible spectrum, using the appropriate annual averaged solar zenith angles and the Rodgers emissivity technique for the infrared. Ozone, above the troposphere, is assumed to act only as an absorber in the visible. In the infrared it is assumed to have a constant-hemispherical emissivity at the “tropopause” temperature (212 K). Surface reflectivities in terms of land and ocean are zonally set and land snow and ocean ice lines are calculated to occur at 273 and 263 K at sea level, respectively.

The response of the model to variations in various climatic determinants is studied, including hemispherical variations in carbon dioxide, aerosol and solar constant, and also including certain zonal variations in man-made thermal energy and aerosol. The model characteristically exhibits a poleward amplification of changes in sea level temperature. Polar zone sea level temperature changes are 2–4 times the hemispherical mean. The sensitivity of the model in terms of the hemispherical mean sea level temperature is about twice that of the globally averaged model of Weare and Snell. It is still more stable than models not incorporating cloudiness as a feedback mechanism. The model exhibits three steady-state solutions when the solar constant is in the range 0.805–0.790 times present day. In this range the solutions with the intermediate sea level temperature for a given value of the solar constant are unstable. All other solutions appear stable.

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